Of 15 patients enrolled in the electrophysiologic protocol for management of patients at high risk for lethal arrhythmias in hypertrophic cardiomyopathy, 4 (27%) have had ventricular tachycardia induced in the absence of medications. Two additional patients exhibited a pro-arrhythmic effect to a Type 1A anti-arrhythmic. Abnormal AV nodal function has been found in 4 patients, and abnormal sinus node function in 2 patients. Re-entrant arrhythmias have been documented in 2 patients, one of whom also had an atrial-ventricular bypass tract.